Yi-Hsien Lee

Two-dimensional atomic crystals of graphene, as well as transition-metal dichalcogenides, have emerged as a class of materials that demonstrate strong interaction with light. This interaction can be further controlled by embedding such materials into optical microcavities. When the interaction rate is engineered to be faster than dissipation from the light and matter entities, one reaches the € strong coupling € regime. This results in the formation of half-light, half-matter bosonic quasiparticles called microcavity polaritons. Here, we report evidence of strong light-matter coupling and the formation of microcavity polaritons in a two-dimensional atomic crystal of molybdenum disulphide (MoS 2) embedded inside a dielectric microcavity at room temperature. A Rabi splitting of 46 €‰± €‰3 €.meV is observed in angle-resolved reflectivity and photoluminescence spectra due to coupling between the two-dimensional excitons and the cavity photons. Realizing strong coupling at room temperature in two-dimensional materials that offer a disorder-free potential landscape provides an attractive route for the development of practical polaritonic devices.

Two-dimensional (2D) materials, such as molybdenum disulfide (MoS ₂ ), have been shown to exhibit excellent electrical and optical properties. The semiconducting nature of MoS ₂ allows it to overcome the shortcomings of zero-bandgap graphene, while still sharing many of graphene's advantages for electronic and optoelectronic applications. Discrete electronic and optoelectronic components, such as field-effect transistors, sensors, and photodetectors made from few-layer MoS ₂ show promising performance as potential substitute of Si in conventional electronics and of organic and amorphous Si semiconductors in ubiquitous systems and display applications. An important next step is the fabrication of fully integrated multistage circuits and logic building blocks on MoS ₂ to demonstrate its capability for complex digital logic and high-frequency ac applications. This paper demonstrates an inverter, a NAND gate, a static random access memory, and a five-stage ring oscillator based on a direct-coupled transistor logic technology. The circuits comprise between 2 to 12 transistors seamlessly integrated side-by-side on a single sheet of bilayer MoS ₂ . Both enhancement-mode and depletion-mode transistors were fabricated thanks to the use of gate metals with different work functions. © 2012 American Chemical Society.

Large-area MoS ₂ atomic layers are synthesized on SiO ₂ substrates by chemical vapor deposition using MoO ₃ and S powders as the reactants. Optical, microscopic and electrical measurements suggest that the synthetic process leads to the growth of MoS ₂ monolayer. The TEM images verify that the synthesized MoS ₂ sheets are highly crystalline. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The two-dimensional layer of molybdenum disulfide (MoS ₂ ) has recently attracted much interest due to its direct-gap property and potential applications in optoelectronics and energy harvesting. However, the synthetic approach to obtain high-quality and large-area MoS ₂ atomic thin layers is still rare. Here we report that the high-temperature annealing of a thermally decomposed ammonium thiomolybdate layer in the presence of sulfur can produce large-area MoS ₂ thin layers with superior electrical performance on insulating substrates. Spectroscopic and microscopic results reveal that the synthesized MoS ₂ sheets are highly crystalline. The electron mobility of the bottom-gate transistor devices made of the synthesized MoS ₂ layer is comparable with those of the micromechanically exfoliated thin sheets from MoS ₂ crystals. This synthetic approach is simple, scalable, and applicable to other transition metal dichalcogenides. Meanwhile, the obtained MoS ₂ films are transferable to arbitrary substrates, providing great opportunities to make layered composites by stacking various atomically thin layers. © 2012 American Chemical Society.